A wireless communication called “millimeter waves” can realize a speed-up of a communication speed utilizing high frequency electromagnetic waves. As a main use of the millimeter wave communication, a short distance wireless access communication, an image transmission system, a simplicity radio, an automobile collision avoidance radar, and the like are exemplified. Also, at present, a technology development of the millimeter wave communication aimed at promotion of utilization such as realization of a large capacity long distance transmission, miniaturization of a wireless apparatus, and reduction in costs is carried out. Here, a wavelength of the millimeter wave is 10 mm to 1 mm and is equivalent to 30 GHz to 300 GHz in frequency. For example, in a wireless communication using the 60 GHz band, as it is possible to perform a channel allocation in units of GHz, an extremely high speed data communication can be carried out.
Also as compared with micro waves widely spread in a wireless LAN (Local Area Network) technology or the like, the millimeter wave has a short wavelength and a strong straight advancing property, and it is possible to transmit an extremely large information amount. In contrast to that, as the millimeter wave has an intense attenuation associated with a reflection, for a wireless path where a communication is carried out, a direct wave or a wave reflected once about the most. Also, as a propagation loss is large, the millimeter wave has such a property that the wireless signal does not reach far.
To compensate the above-mentioned flying distance problem of the millimeter wave, a method is conceivable that an antennal of a transreceiver is set to have a directivity, and a transmission beam and a reception beam thereof are directed toward a direction in which the communication party is positioned to extend a communication distance. The directivity of the beam can be controlled, for example, by providing a plurality of antennas respectively to the transreceivers and changing a transmission weight or a reception weight for each antenna. In the millimeter wave, as the reflected wave is hardly used and the direct wave becomes important, a beam-shaped directivity is suitable, and it is conceivable to use a sharp beam for the directivity. Then, after a training on an optimal directivity of the antenna is conducted, the millimeter wave wireless communication may be carried out.
For example, a wireless transmission system is proposed in which after a signal for deciding a directivity direction of the transmission antenna is transmitted by second communication means utilizing a communication based on one of a power line communication, an optical communication, and an acoustic communication to decide the direction of the transmission antenna, a wireless transmission between the transreceivers is carried out by first communication means using radio waves equal to or higher than 10 GHz (for example, see PTL 1).
Also, a method of extending the communication distance by utilizing the directivity of the antenna is applied to IEEE802.15.3c that is a standard for a wireless PAN (mmWPAN: millimeter-wave Wireless Personal Area Network) using the millimeter-wave band.
However, according to the method of extending the communication distance by utilizing the directivity of the antenna, an adverse effect exists that an improvement in the transmission reception power of millimeter wave signals in a direction of a particular communication party can be observed, but the millimeter wave signals do not reach the peripheral station that does not exist in the direction. For example, when a control signal such as a beacon for effecting a coordination is transmitted to a plurality of communication stations at the same time with a control frame, it is obvious that the directional communication is not appropriate. Also, according to the directional communication, the communication link is easily invalidated along with a travel of the communication station, and a situation may occur that a desired communication cannot be carried out by any means.
For example, a wireless terminal apparatus is proposed which is provided with position information obtaining means such as a GPS (Global Positioning System) unit, obtains position information of its own apparatus, and also exchanges mutual position information with the communication party to control the directivity of the directional antenna for performing a long distance data transmission by millimeter waves (for example, see PTL 2). According to the same wireless terminal apparatus, even when the positional relation with the communication party is fluctuated, it is possible to escape from a situation in which the communication cannot be carried out by exchanging the position information and adjusting the directivity of the antenna, but it is necessary to increase apparatus costs along with the mounting of the position information obtaining means and implement a communication procedure for exchanging the position information with the communication party. Also, the same wireless terminal apparatus is configured to transmit the data with the radio waves of the millimeter-wave band having a broadband performance and transmit control information with the radio waves of microwave band, but as only a path search processing is carried out on the control line, the coordination cannot be effected.